1. Field of the Invention
This invention relates to an electrophotographic organic photosensitive material to be used in a copying machine, a laser printer, etc. More specifically, it relates to an electrophotographic organic photosensitive material capable of positive charging or both the positive and the negative chargings and having an improvement in sensitivity and residual potential.
2. Description of the Prior Art
For electrophotographic copying using a digital optical system a light source having a wavelength of usually at least 700 nm is used. Organic photosensitive materials (OPC), amorphous silicon (.alpha.-Si) and some selenium photosensitive materials are known as photosensitive materials having a sensitivity in this wavelength region. From the overall viewpoint of sensitivity and cost, OPC is used mostly in this field.
Although there are many so-called function separation-type organic photosensitive materials, i.e. laminated-type photosensitive materials, obtained by laminating a charge generating layer (CGL) and a charge transporting layer (CTL) as organic photosensitive material, there has been already known a single layer dispersed type organic photosensitive material wherein a charge generating substance is dispersed in a medium of a charge transporting substance.
A charge generating substance of this kind of photosensitive material having a high carrier movability is required. But since the charge transporting agent having a high carrier movability are mostly a positive hole transporting, what is actually used is limited to negative chargeable organic photosensitive materials. However, as the negative chargeable organic photosensitive materials utilizing a negative polarity corona discharging, there is much ozone development and it contaminates the environment. A problem of degradation of the photosensitive materials also arises. To prevent them, particular charging systems are required such as a particular charging system of not generating ozone, a system of decomposing the generated ozone and a system of evacuating ozone within the apparatus, and this has the defect of complicating the process or systems.
There has been proposed in the Japanese unexamined patent publication No. 206349/89 a compound having a diphenoquinone structure as a charge transporting agent for an electrophotographic sensitive material which is exemplified as a rare charge transporting substance having an electron transportability.
The diphenoquinone mentioned above has good compatibility with a binder resin, and is said to show good electron transporting ability. However, the laminated photosensitive material having this diphenoquinone derivative still is defective of not having either a high residual potential or a sufficient sensitivity for practical application.
On the other hand, as regards the charging polarity of a photosensitive material, if it can be used both in positive charging, further, if it can be used in both the positive charging and the negative charging, the range of application of the photosensitive material can further be broadened, and it may be markedly advantageous in removing many above-mentioned defects. Furthermore, if the organic photosensitive material can be used in a single layer dispersion-type, it facilitates a production of the photosensitive material and many advantages can be achieved in preventing the occurrence of film defects and improving optical characteristics.